This invention relates to pneumatic tire manufacture and more particularly to a cutting apparatus for cutting ply stock material which is employed in the construction and manufacture of pneumatic tires.
In the manufacture of pneumatic tires, one of the principal materials used to build the tire carcass is a thin sheet of uncured rubber-like material known as a fabric, building ply or ply stock. In the manufacture of such ply stock, parallel cords of fabric, wire cord or high strength cord such as Kevlar cord are passed through a pair of rolls in cooperation with calendering rolls which work and calendar unvulcanized rubber onto the parallel cords as they pass through the pinch rolls to form a continuous sheet of material with the parallel strands of cord embedded therein and running in a direction that is parallel to the longitudinal centerline of the material. Thereafter, such sheet material is cut into sections of fabric which sections may have the cords at a bias angle relative to the cut edge. The cut sections are then spliced together to make a building ply or ply stock with cords therein located at a desired angle relative to the longitudinal centerline of the ply stock. Such stock or ply stock may also be at a ninety degree angle to the longitudinal centerline of the ply stock formed; however, for purpose of this description and example, the invention will be described wherein the cords are at some small acute angle relative to the longitudinal centerline of the ply stock. Layers of ply stock are applied to a tire building drum in such a manner that cord members of overlapping plies crisscross with respect to the cord members above or below. The tire beads are then set against the ends of the ply stock and the plies are turned thereover. Additional plies, chafer strips, sidewall strips, breakers, overhead belts and a tread ply may be applied in varying orders, and stitched thereto. Such carcass is substantially a cylindrical band. The angle measured between the cords and the circumferential line around the crown of the tire determines the bias angle of the plies. In the case of conventional bias ply pneumatic tires, this may be approximately sixty degrees. However, this apparatus can cut fabric material with strands of steel or Kevlar cord therein which make a small acute angle with the circumferential centerline of the tire. After the removal of such green tire, the tire is given a toroidal shape on a second step machine and then vulcanized. The shaping on the second step machine changes the bias angle. The above description contemplates the use of inextensible or non-extensible cord materials such as nylon, Kevlar cord and wire. In the processing of ply stock containing such inextensible cord, processing is difficult because of the tremendous strength of the material, which cutting is particularly compounded by the very low bias angle cutting on such stock wherein the cutters tend to fray the ends of the Kevlar cord or wire, which action interferes with the splice to be effected. The use of the present apparatus permits the cutting of stock which has a zero bias angle, as where the cords are ninety degree relative to circumferential center line around the crown of the tire.
In bias cutting rubberized fabric, the conventional way of cutting is to use a pair of steel fingers that lift the fabric away from the conveyor belt on which it travels, so that a rapidly rotating cutter disk is above the fingers but is cooperative therewith to cut the fabric. The application of this conventional apparatus to cut rubberized Kevlar and steel cord fabric including fabric for radial tires is difficult and unsatisfactory. The cutter of the present invention is mounted on a carriage and moveable bodily therewith. As the carriage and cutter are moved linearly, the cutter frictionally contacts the material and rolls along cutting the material. The cutter is hollow ground and is cooperative with an anvil also moveable with the carriage. An insert on the anvil has a tapered cutting edge that cooperates with the rolling cutter which has a circular cutting edge, whose edge tapers in a direction that insures a positive shearing action. Upon the completion of a cut across the fabric material, the cutter and anvil are pivoted out of the way so that the cutter and anvil can be returned to their starting position as the fabric material is advanced or indexed in preparation for the succeeding cut.